Electric oscillator



Nov. '24,.1942. K. J. G ERMEsHAU SEN 2,302,690

ELECTRIJCOSCILLATOR Original Filed-March 9, 1937 INVENTOR ATTORNEYPatented Nov. 24, 1942 ELECTRIC OSCILLATOR Kenneth Joseph Germeshausen,

Cambridge, Mass.

Original application March 9, 1937, Serial No.

Divided and this application October 6, 1937, Serial No. 167,618

24 Claims.

The present invention relates to electric oscillators, and moreparticularly to oscillators of the multi-vibrator type. The presentapplication is a division of application, Serial No. 129,837, filedMarch 9, 1937, Patent No. 2,201,166 granted May 21, 1940.

An object of the present invention is to provide a novel electricoscillator.

A further object of the invention is to provide a novel oscillator forcontrolling the flashing rate of a stroboscopic lamp.

Another object is to provide a novel method of controlling thefrequency.

Still another object of. the invention is to provide a novel means forcalibrating the frequency scale of the above oscillator.

Other objects will be explained hereinafter and will be particularlypointed out in the appended claims.

' For a consideration of what I believe to be .novel and my invention,attention is directed to the accompanying description and the claimsappendedthereto.

The single figure of the accompanying drawing is a circuit diagramillustrating a preferred complete stroboscope circuit, with .aconventional power supply to furnish direct current from thealternating-current mains, a. separate oscillator embodying theinvention for driving the stroboscopic lamp so as to cause the lamp toflash at the desired frequency, means for calibrating the,

oscillator, means for operating the lamp so as to cause it to flash atthe frequency of the alternating-current supply voltage from the line,and a contactor device for controlling the flashing rate.

The tube I may be of the type illustrated in my application, Serial No.48,669, filed November 7, 1935, Patent No. 2,185,189 dated January 2,1940, or a modification of the same, illustrated in Fig. 1 and describedmore at length in a copending application, Serial No. 129,838, filedMarch 9, 1937, Patent No. 2,201,167 dated May 21, 1940. It comprises anevacuated glass envelope-filled with a suitable gas, suchas neon, or anyof the other noble gases, such as argon or helium. The pressure of thegas in the tube may vary, the usual pressure being from one to twocentimeters. The tube contains several electrodes, namely, a solidcathode 2, an anode or plate 5, and one or more grids, inner and outergrids being shown at 3 and 4 between the anodeand the cathode. The grid3 is at zero potential with respect to the cathode 2 and the grid 4 ispositive with respect to the grid 3. The source of the electrons is abright cathode spot on the surface of the cathode.

Either grid may be usedas the control grid, depending upon the polarityand the magnitude of the control voltage.

As explained in the said Patent No. 2,185,189, the grid 3 may, in normaluse, he placed close to the cathode 2, say-,xnot more than a, fewmillimeters from the cathode, and may be of such shape that the cathodewill sputter a thin surface layer or coating of a material of lowwork-function, such as caesium, on the grid surface during the normaloperation of the tube. A-thin surface coating or layer of the caesium orother material of low work-function is thus maintained on the grid 3. Asexplained in the said Patent No. 2,201,167, however, the grid 3 may,under some circumstances, be precoated.

The form of the arc stream between the anode and the cathode is a columnof small diameter which has high intrinsic brilliance, withsubstantially all the light emitted from the concentrated arc stream.This discharge is easily distinguished from a glow discharge, whichoccupies substantially the whole interior of the tube, with a dischargeof low intrinsic brilliance, the greatest brilliance being at thesurface of the cathode.

In the illustrated stroboscopic circuit, the anode 5 and the cathode 2of the tube are shown connected across a condenser H, which iscontinuously charged, by way of conducting wires 1 and 8, from asuitable direct-current source of, say, 300 to 400 volts, connectedthrough a variable current-limiting impedance l2, which may be aresistor, or a-combination of resistance and inductance. The source maybe constituted of thermionic. or gaseous-discharge rectiflers forproducing direct current from alternating curcathode 2 and the grid 3.

rent, as illustrated, or any other-source of direct current.

In the illustrative circuit, a transformer 18, a double-anode rectifiertube 11 and a condenser 69 form a conventional power supply to give anydesired direct-current voltage, say, 300 volts, from the 110-voltalternating-current mains.

The discharge condenser II is used for highfrequencyoperation of thestroboscope circuit; for low-frequency operation, a condenser I3 isconnected in parallel with the condenser II by means of a switch 66.

Impedances l9 and are shown connected between the cathode 2 and the grid4, and between the grid 4 and the anode 5, respectively; and animpedance 8| is shown connected between the The bias is so adjusted onthe grid 4 by means of these impedances, which may be resistors, and thesupply the voltage between the anode 5 and the cathode 2 much greaterthan the voltage required to cause a glow discharge between the grid 4and the grid 3,v and the tube will thus stay-in a non-conducting statewhen the condenser I I is fully charged. The lamp circuit comprises thesaid two discharge condensers II and I3, the said currentlimitingresistor I2 and the three resistors 8|, 80 and 18. v

Current is also supplied from the power supply to conductors I00 andI32. The conductor I32 is connected, through a resistor I24, to a switch88, adapted to occupy two positions A and B. The conductor I 00 isconnected, by a contactor device 81, to a contact member with which theswitch 88 is adapted to contact in position B. The circuits of thehereinafter-described multivibrator are open when the switch 88 occupiesthe position B. The switch 88 is connected by a conductor 58,

through a condenser 83, to the grid 3. The switch 88 is connected alsoto the source of alternating current, by way of a conductor 20, andthrough a resistor 84, by a switch 85. The contactor 81 maybeperiodically opened and closed in any desired manner; that is notshown in order to simplify the drawing.

With the switch 88 in position B, and the switch 85 open, the lamp I canbe triggered at the desired instant by means of the contactor device 81,which causes a momentary surge through the condenser 83. When thecontactor device 81 closes, therefore, the grid 3 is given a negativevoltage pulse equal to the voltage existing between the conductors I00and I32. The condenser 83 then discharges through the resistor 8| andthe grid 3 to the cathode 2, allowing the voltage of the grid 3 toreturn to zero. The discharge circuit extends from one side of thecondenser 83, through the resistor 8I and the grid 3 and the cathode 2,in parallel, by way of the conductors 8, 85 and I00, and through theswitches 81 and 88, the latter in the position B, to the other side ofthe condenser 83. Once the contactor 81 becomes closed, it may remainclosed without the stroboscope flashing on again when the condensers IIand I3 build up their voltages. The operation is independent of thelength of time that the contactor 81 remains closed, the

complete function being performed at the moment it first becomes closed.The contactor 81, therefore, gives only one impulse of voltage at eachclosing, and the length of time the contactor 81 remains closed does notaffect the operation of the tube.

The voltage applied between the grids 3 and 4 should be sufllcient tocause an initiating glow discharge between the grid 4 and the coating onthe grid 3. The voltage at which this discharge takes place is low andsubstantially constant, due to the fact that the grids 3 and 4 shieldthe field between the grids from charges on the glass. To start the glowdischarge between the grids may require a voltage of only about ahundred volts and a current of only a fraction of a mililampere, so verylittle power is required.

The use of the controlling oscillator, for impressing its oscillationsupon the grid 3, makes it possible to operate the stroboscope withoutany moving parts.

The illustrated multivibrator oscillator is simple and cheap, itpossesses constancy of frequency irrespective of variations in appliedvoltage and an abrupt or saw-tooth wave form, and it has a comparativelyhigh voltage output. The directcurrent power supply for the oscillatormay be obtained from the power supply for the stroboscope circuitthrough conductors 84 and and a resistor 81. A filter condenser 88 isprovided to remove any slight alternating-current ripple in thedirect-current voltage.

The oscillator circuit comprises a pair of electron-discharge vacuumtriodes 88 and 88, a pair of anode or plate resistors or otherimpedances I22 and I 24, the grid resistors or other impedances I38 andI38 that are connected to the grids or control electrodes I I4 and I I8of the triodes 88 and 88, the grid condensers or electron-storagedevices I25, I28, I21 and I28, and the condenser I28. Thefrequency-control circuit of the said oscillator comprises the variable,calibrating resistors or other impedances I2I and a biasing source ofenergy. The biasing source of energy is illustrated as comprising thepotentiometer I I8. The set of electrodes of the vacuum triode 88,comprising the filament or cathode 88, the grid or control electrode H4and the anode 82, and the set of electrodes of the vacuum triode 88,comprising the filament or cathode 88, the grid or control electrode II8 and the anode 84, may be in separate envelopes, or in a singleenvelope. It is usually more convenient to combine the two in a singletube. ,The voltage from the voltage source is applied to the oscillatorby way of the conductors I00 and I32, between which the oscillator isconnected. The calibrating resistor |2| is'connected between resistor 81and conductor I32. The second calibrating resistor I30 is connected, inseries with the potentiometer I I8, to the conductor I00. Thepotentiometer H8 is thus connected between the calibrating resistors I2Iand The cathodes of the oscillator tubes 88 and 88 are connected to theconductor I00. The anodes of the oscillator tubes are connected to theconductor I32 and the resistor I2I through the resistors I22 and I24.The pair of resistances I22 and I24 thus connect the anodes 82 and 84,respectively, to the upper end of the potentiometer I I8, which ispositive with respect to the cathodes 88 and 88 by reason of the factthat it is connected by the conductor 84, through the resistor 81, tothat terminal of the rectifier 11 that is positive with respect to theircathodes. The resistor I22 and I24, therefore, maintain the anodes 82and 84 positive with respect to the cathodes. The switch 86 isconnected, in position A, to the anode 84 of the triode 88. The anodes82 and 84 are thus connected to one side of the source of voltage by theconductor I32, through the resistances I22 and I24. The cathodes 88 I33,through the resistor I38, to the grid II4.

The input circuit of the triode 88 may similarly be traced from thefilament 88, by way of the conductor I00, through the calibratingresistor I30, the lower portion of the potentiometer H8, and theadjustable arm I34, and by way of the conductor I33, through theresistor I38, to the grid II8. One of the ends of each of the respectiveresistances I38 and I38 is thus connected other ends are connected to apotential position' with respect to the cathodes 96 and 98, byway of theconductor I33, to the adjustable arm I34 ofthe potentiometer H8. Thesaid other ends of the resistors I 36 and l38 are thus maintainedpositive with respect to the cathodes 96 and 98; The output circuit ofthe triode 89 may be traced from the filament 96, by way of theconductor I00, through the calibrating resistor I30, the potentiometerH8, and the calibrating resistor I2I and, by way of the conductor I32,through the resistor I22, to the anode 92. The output circuit of thetriode 88 may similarly be traced from the filament 98, by way of theconductor I00, through the calibrating resistor I30, the potentiometerH8 and the calibrating resistor I2I and, by way of the conductor I32,through the resistor I24, to

the anode-94, =The condenser I isconnected between the [grid II6 of theelectron-discharge device 88 and the anode 92of the electron-dischargedevice 89, and the condenser I26 may be connected in parallel therewith.The condenser I2! is similarly connected between the grid I I4 of theelectron-discharge device 88 and the anode 94 of the electron-dischargedevice 88, and the condenser I28 maybe connected in parallel therewith.

With the switch 86 in the position A, the output of the oscillator,taken from the plateof one of the triodes, is connected to thestroboscopic lamp I through the coupling condenser83 and the conductor58.

The principles of operation of .the oscillator and its production of asaw-tooth wave form are" well understood in the art and hence will notbe gone into here. In the usual oscillator, the conductor I33, joiningthe ends of the grid resistors I36 and I38, is connected to the cathodecircuit of the triodes, represented by the conductor I00. The frequency,of the oscillator is then varied by varying the resistors I36 and I38.Since the resistors I36 and I38 are of considerable magnitude (say, 1megohm), they are not conveniently procurable in the variable form and,furthermore, varying these resistors gives a non-linear frequency scaleof the exponential type.

According to the present invention, the frequency of the multivibratoris controlled linearly by adjusting the slider I34 back and forth on thepotentiometer II8 to vary the positive bias on the grids of the triodes88 and 89 in a linear fashion. This yields not only a linear frequencyscale and a wide frequency range,as much as six to one.

- The potentiometer I I6 is calibrated in flashes per minute of thestroboscope lamp, with the aid of a vibrating reed I40 and thecalibrating resistors I2I and I30. It has a direct-reading scale offrequency against resistor setting, instead of an exponential scale, asformerly obtained. Asomewhat greater frequency range occurs, moreover,with reasonable values of resistance in the potentiometer II8.

The potentiometer H8 is provided with two linearly calibrated oruniformly divided scales (not shown), with a four-to-one factor betweenthem. The frequency of the oscillator is shifted by this factor by meansof the condensers I26 and I28. Connecting these condensers in thecircuit by means of their accompanying switches reduces the frequency ofthe oscillator and shifts the whole frequency scale in linear fashion,the amount of the shift depending on the values of the condensers. Thestroboscope may have a I22 with condenser I25, and the time constant ofresistor I24 with condenser I21, be appreciably less than the shortestinterval between oscillations at the high-frequency end of the scale.The condenser I29 may be connected across the conductors I00 and I32, inparallel with the resistors I2I and I30 and the potentiometer II8, tocorrect a slight curvature at the lower end of the scale.

There is a tendencyfor the scale or scales (not shown) to have a furtherslight curvature in the region of operation of the oscillator with thebias voltage on the grids at the lower end, near the zero, of the scale.This may be corrected for by having the minimum value of the resistorI30 not less than about ten per cent of the potentiometer I I8. Inactual practice, the variation in frequency per unit adjustment of theslider I34 may be slightly greater or less than that indicated on thescale. sistors I2I and I 30, however, serve to adjust the calibration ofthe frequency scale by matching the oscillator to the scale. Theresistor I2I adjusts the frequency of the oscillator at the high end ofthe scale to correspond to the scale markings (not shown), withoutappreciably affecting the lower end of the scale, and the resistor I30similarly adjusts the lower end of the scale, without affecting thehigher end. Both resistors I2I and I30, at their respective ends of thescale, serve to adjust the rate at which the frequency of themultivibrator changes in response to changes in the applied biasvoltage. By means of these resistors it is possible so to calibrate theoscillator as exactly to match the frequency to the linearly calibratedscale provided, regardless of slight variations in the oscillatorcircuit due to manufacturing errors or aging of the parts.

The invention also provides a means for checking the calibration'of theoscillator. According to the specific embodiment of the invention thatis illustrated and described herein, the checking apparatus comprisesthe vibrating reed I43, driven by means of a solenoid I42 in exactsynchronism with the alternating current of the line. To this end, thesolenoid I42 is connected in circuit with a switch I44 and conductorsI46 and I48 across the alternating-current supply. At most localities,the frequency of the alternating mains is controlled with suflicientaccuracy to enable the vibrating reed I 40 to serve as a standard. Thereed is placed so that the light from the flashing lamp falls upon it sothat, when the flashing rate of the lamp is the same as the frequency ofthe reed, the reed appears to stand still. When this occurs, the sliderI34 of the potentiometer III should be at a marked calibrating point. Ifit is not, it may be brought to the proper point by adjustments of thecalibratingresistors I2I and I30. The check is easily and quickly madeand serves to compensate for factors that may impair the calibration.-The resistors I2I and I30, as before explained, enable setting offrequency of the oscillator in terms of the 60-cycle reed I40 tocorrespond to the scale markings at both ends of the scale, withoutdisturbing the linear variation of frequency with adjustment of theslider I34 over the potentiometer H8. The resistors I2I and I33 may besaid to serve the function of so tipping the whole frequency scale thatthe value, say 3600, checked at one frequency by means of the reed I40shall correspond to all frequencies The before-mentioned variable re-'throughout the length of the scale. Uniform rate of change of frequencycorresponding to the adjustment of the slider I34 is thus preservedthroughout the length of the scale.

An alternative method of checking the calibration is shown by a glowlamp I50 and a resistor I49, connected in series to thealternating-current supply at one anode of the rectifier I1 and to theanode 5 of the stroboscope lamp. When the frequency of thealternating-current supply and the stroboscope are the-same and inphase, the glow lamp will be extinguished. When the frequency isslightly different, the glow lamp will go on and off at a rate equal tothe difference in frequency. This is the familiar beat method ofmatching frequencies.

By closing the switch 85, an alternating-current voltage is applied tothe oscillator from the transformer 18 through the resistance 84 and theconductor 20. This causes the oscillator to run at the frequency of theline voltage and in exact synchronism therewith. This is useful incertain applications of the stroboscope.

The light produced by this stroboscope, obtained from a 115-volt,60-cycle alternatingcurrent source, is sufficient to permit goodstroboscopic observation of mechanisms, particularly when the light isconcentrated by means of a parabolic reflector. Because of thecalibrated frequency scale, the stroboscope is particularly useful inmeasuring the speed of rotating or vibrating mechanisms.

Modifications will occur to persons skilled in the art, and all such areconsidered to fall within the scope and spirit of the invention.

What is claimed is:

1. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers conn cted, re-

spectively, between the grid of each of the sets and the impedance ofthe other set, and means for adjusting the potentiometer to vary thebias on the grids in order to control the frequency of themultivibrator.

2. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, and input circuit connectrd between thefilament and the grid of each set. an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes. a potentiometerconnected in both output circuits, two condensers connected,respectively, between the grid of each of the sets and the impedance ofthe other set, and a variable impedance connected between one end of thepotentiometer and the filaments.

3. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set. an output circuit connected betweenthe filament and the plate of each set, an impedance c nnected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits, two condensers connected,respectively, between the grid of each of the sets and the impedance ofthe other set, and a variable impedance connected between one end of thepotentiometer and the plates.

4. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a late, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits, two condensers connected,respectively, between the grid of eachof the sets and the impedance ofthe other set, and a variable impedance connected between one end of thepotentiometer and the plates in series with the respective twofirst-namedimpedances.

5. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, 9. potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of each of the setsand the impedance of the other set, means for adjusting thepotentiometer to vary the bias on the grids in order to controlthefrequency of the multivibrator, and a variable impedance connectedbetween one end of the potentiometer and the filaments.

6. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of each of the setsand the impedance of the other set, means for adjusting thepotentiometer to vary the bias on the grids in order to control thefrequency of the multivibrator, and means for calibrating thepotentiometer.

'7. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament andthe grid of each set, an output cir-' cuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively,

between the grid of each of the sets and the impedance of the other set,means for adjusting the potentiometer to vary the bias on the grids inorder to control the frequency of the multivibrator, means forcalibrating the potentiometer, and means for adjusting the calibration.

8. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of each of the setsand the impedance ofthe other set, means for adjusting the potentiometerto vary the bias on the grids in order to control the frequency of themultivibrator, and means for calibrating the potentiometer comprising avariable impedance connected between one end of the potentiometer andthe filaments.

9. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of each of the setsand the impedance of the other set, means for adjusting thepotentiometer to vary the bias on the grids in order to control thefrequency of the multivibrator, means for calibrating the potentiometer,and means for checking the calibration.

10. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of each of the setsand the impedance of the other set, means having a scale for changingthe frequency of the multivibrator, a vibrating member, and means foradjusting the scale of the frequency-changing means in accordance withthe vibrations of the vibrating member.

11. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of th sets of electrodes,

plate of each set, an impedance connected in the output circuit of oneof the sets of electrodes, an impedance connected in the output circuitof the other-set of electrodes, two condensers connected, respectively,between the grid of each of the sets and the impedance of the other set,and means for applying an adjustable positive voltage to the inputcircuits ,to adjust the frequency of the multivibrator. 13. Amultivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between theanadjustable positive voltage across the potenan impedance connected inthe output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, twocondensers connected, respectively, between the grid of" each of thesets and the impedance of the other set, means for adjusting thefrequency of the multivibrator, a vibrating member energized to vibrateat a predetermined frequency, and additional means for adjusting theoutput frequency of the multivibrator, thereby to calibrate the outputfrequency of the multivibrator.

12. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the tiometer to apply an adjustable positive voltage tothe input circuits, thereby to adjust the fre-,

quency of the multivibrator.

14. An electric system comprising an oscillator having an input circuitand an output circuit, a source of alternating voltage, and means forcalibrating the oscillator comprising a glow lamp connected to theoutput circuit and the source.

15. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes,

an impedance connected in the output circuit oi! the other set ofelectrodes, a potentiometer connected in both output circuits to biasthe grids positively, two condensers connected, respectively, betweenthe grid of each of the'sets and the impedance of the other set, andmeans for adjusting the potentiometer to vary the bias on the grids in alinear fashion in order to control the frequency of the multivibratorlinearly.

16. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits to bias the grids positively, a scaleassociated with the potentiometer, and two condensers connected,respectively, between the grid of each of the sets and the impedance ofthe other set, the'time constant of each condenser and the impedance towhich it is connected being appreciably less than the shortest intervalbetween oscillations. at the high-frequency end of the. scale.

17. A multivibrator comprising two sets of electrodes, each comprisingprincipal electrodes, namely, a filament and a plate, and also a grid,an input circuit connected between the filament and the grid of eachset, an output circuit connected between the filament and the plate ofeach set, an impedance connected in the output circuit of one of thesets of electrodes, an imother set of electrodes, a potentiometerconnected in both output circuits, two condensers connected,respectively, between the grid of=each of the sets and the impedance ofthe other set, and an impedance connected between one end of thepotentiometer and one of the principal electrodes.

18. A multivibrator comprising two sets of electrodes, each comprising afilament, a grid and a plate, an input circuit connected between thefilament and the grid of each set, an output circuit connected betweenthe filament and the plate of each set, an impedance connected in theoutput circuit of one of the sets of electrodes, an impedance connectedin the output circuit of the other set of electrodes, a potentiometerconnected in both output circuits, two condensers connected,respectively, between the grid of each electrode of the other dischargedevice, a pair of resistances, means for connecting one end of eachresistance to said control electrodes, and means for maintaining theother ends of said pair of resistances positive with respect to saidcathodes and negative with respect to said anodes.

20. An oscillator for producing a saw-tooth wave form comprising a pairof electron discharge devices each of which includes a cathode, acontrol electrode, and an anode, means including anode resistances formaintaining said anodes positive with respect to said cathodes, meansincluding electron storage devices for connecting the anode of eachdischarge device to the control electrode of the other discharge device,and

means including a pair of resistances for con-- necting saidcontrol'electrodes to a source of potential positive with respect tosaid cathodes.

21. An oscillating circuit for producing a sawtooth wave form comprisinga pair of electron discharge tubes each including an anode, a controlelectrode, and a cathode, means including a pair of resistances forconnecting said anodes to a source of potential positive with respect tosaid cathode, a condenser connected between, the anode of each tube andthe control electrode of the other tube, a resistance connected to thecontrol electrode of each tube, and means for connecting the other endof the control electrode resistances to a potential positive withrespect to said cathodes.

22. A multivibrator comprising two sets of electrodes, each comprising acathode, a control electrode and an anode, an input circuit connectedbetween the cathode and the control electrode of each set. an outputcircuit connected between the cathode and the anode of each set, animpedance connected in the output circuit of one of the sets ofelectrodes for maintaining the anode of the said one set of electrodespositive with respect to the cathode of the said one set of electrodes,an impedance connected in the output circuit of the other set ofelectrodes for maintaining the anode of the said other set of electrodespositive with respect to the cathode of the said other set ofelectrodes, two condensers connected, respectively, between the controlelectrode of each of the sets and the anode of the other set, and meansfor energizing the output circuits and for applying an adjustablepositive voltage bias on the control electrodes in order to control thefrequency of the multivibrator.

23. A multivibrator comprising two sets of electrodes, each comprising acathode, a control electrode and an anode, an input circuit connectedbetween the cathode and the control electrode of each set, an outputcircuit connected between the cathode and the anode of each set, animpedance connected in the output circuit of one of the sets ofelectrodes for maintaining the anode of the said one set of electrodespositive with respect to the'cathode of the said one set of electrodes,an impedance connected in the output circuit of the other set ofelectrodes for maintaining the anode of the said other set of electrodespositive with respect to the cathode of the said other set ofelectrodes, two condensers connected, respectively, between the controlelectrode of each of the sets and the anode of the other set, means forenergizing the output circuits and for applying an adjustable positivevoltage bias on the control electrodes in substantially linear fashionin order to control the frequency of the multivibrator substantiallylinearly, and means for adjusting the rate at which the said frequencychangesdn response to changes in the applied bias voltage.

24. A multivibrator comprising two sets of elec trodes, each comprisinga cathode, a control electrode and an anode, an input circuit connectedbetween the cathode and the control electrode of each set, an outputcircuit connected between the cathode and the anode of each set, animpedance connected in the output circuit of one of the sets ofelectrodes for maintaining the anode of the said one set of electrodespositive with respect to the cathode of the said one set of electrodes,an impedance connected in the output circuit of the other set ofelectrodes for maintaining the anode of the said other set of electrodespositive .with respect to the cathode of the said other set ofelectrodes, two condensers connected, respectively, between the controlelectrode of each of the sets and the anode of the other set, means forenergizing the output circuits and for applying an adjustable positivevoltage bias on the control electrodes in substantially linear fashionin order to control the frequency of the multivibrator substantiallylinearly, the last-named means including an impedance, and means forvarying the last-named impedance to adjust the rate at which the saidfrequency changes in response to changes in the applied bias voltage.

KENNETH J, GERMESHAUSEN.

